The present invention relates generally to techniques for testing physical properties of compositions of matter and more specifically to a technique for achieving repeatability in testing the gel point of an epoxy resin.
Many electronic component parts, such as printed circuit boards, use epoxy resins in their fabrication. Of great practical significance to processes using epoxy resins to fabricate these parts is the point at which a given epoxy resin becomes plastic, often known as gel point. It is common to measure the time required for a given epoxy resin to reach the gel point at a predetermined temperature. It can be shown that this gel point (time) for an epoxy resin changes from one production run to another and through storage conditions. Therefore, laboratory testing of each batch of epoxy resin is required prior to use in a further production step.
To date, the Fisher method of testing gel point time is the most popular. The method involves grinding the sample to be tested into a fine powder. The sample is placed on a metallic holder which has been heated to a predetermined temperature. The laboratory technician manually stirs the sample until he visually observes that the gel point has been reached. The technician also times the process manually with a stop watch. Because this manual process varies greatly from technician to technician, the results tend to vary greatly. A further problem is that since the test environment is essentially that of the laboratory, changes in ambient conditions greatly effect measured results.